A liquid crystal display apparatus including a liquid crystal panel as a display panel is thin and lightweight, and has low power consumption. For this reason, in recent years, the liquid crystal display apparatus is widely employed as an image display apparatus of a television receiving apparatus, a computer, and a mobile terminal.
The liquid crystal panel which is a component member of the liquid crystal display apparatus does not emit light itself. Thus, unlike a self luminous display apparatus such as a cathode ray tube (CRT), the liquid crystal display apparatus needs a planar light source unit.
As one system of light source units, there is an edge light system. The edge light system is a system in which a light guide plate and a cover to support the light guide plate are disposed on a back side of the liquid crystal panel, and a light source is disposed on a side face side of the light guide plate. The edge light system emits light which comes through the side face of the light guide plate from one surface of the light guide plate while diffusing the light in the light guide plate. Therefore, the edge light system has an advantage capable of reducing the front to back thickness of the display apparatus, compared with a direct light system in which the light source is disposed on the back side of a diffusion plate.
The edge light system, in recent years, has come to use a light emitting diode (LED) smaller than a conventional cold cathode tube as a light source. An LED used as the light source is an LED emitting white light. The white LED has a variation in emission characteristics such as chromaticity or luminance for each LED. Therefore, the manufactured white LEDs are managed by being divided into a plurality of groups with respect to characteristic values. Each group is referred to as a rank. When mounting the white LED, if white LEDs having different ranks are mounted in combination, the display quality deteriorates, and therefore it is necessary to mount the white LEDs with the same rank on an LED substrate.
Further, in such a case that the LED substrate which has been mounted and used is exchanged or repaired (that is, maintained) due to failures thereof, an LED substrate on which the white LEDs having the same rank as the white LEDs mounted on the failed LED substrate is required to be found. However, finding this from a plurality of manufactured LED substrates is a difficult task requiring a great deal of effort.
In order to solve the above-described problem, Japanese Patent Application Laid-Open No. 2011-18576 describes a display apparatus in which ranks of a plurality of white LEDs are recorded on a surface of each LED substrate on which the white LEDs are mounted or side faces of the white LEDs, each time the LED substrate is manufactured. In the above-described display apparatus, when the LED substrate fails, the rank of the white LEDs mounted on the LED substrate may be obtained by reading a bar code recorded on the failed LED substrate.